JPS6375685A - Synthetic apparatus radar - Google Patents

Abstract

PURPOSE:To diversify the practical use of a system, by adding a spectrum analyzer changing in its analytical accuracy, a mode controller and a beam controller etc. CONSTITUTION:A beam controller 14 controlling the direction of the beam emitted from an antenna 1 and the step converting FFT15 of a spectrum analyser stepwise enhanced in its analytical accuracy corresponding to the increase in the length of a synthetic aperture are controlled by the angle signal corresponding to the mode outputted from a mode controller 16 corresponding to set practical use to enhance the azimuth resolving power of a receiving signal set to high distance resolving power by a pulse compressing apparatus 4. By this method, the image pickup of the surface of the earth corresponding to a real time mode, a scanning mode, a high resolving mode and a zoom mode different in the length of an aperture corresponding to a practical use request is performed by a flight body such as a satellite. As a result, the practical use of a synthetic aperture radar system is diversified.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is an improvement of a synthetic aperture radar that is mounted on a flying object such as an artificial satellite or an aircraft and obtains high-resolution images of the ground surface, sea surface, etc. It is related to.

[Conventional technology]

FIG. 7(a) and tbl are, for example, F, T, Ula
by, R.

Paper by K. Moore, A. K.)'ung Microwave Remote Sensi
ng (Active and Pa5sive)-
? Microwave remote sensing (active and passive) JP, P, 630
~745, Addition-Wesley p
ublishing Company.

1 is a block diagram showing the configuration of a conventional synthetic aperture radar disclosed in (1982). In each figure, 1
is the antenna, 2 is the transmitter, 3 is the receiver, 4 is the pulse compression back d, 5 is the phase compensation device, 6 is the FF T (Fast
Fourier Transformer (Fast Fourier Transformer), 7 is a display, 8 is an inertial navigation device, 9 is an antenna drive device, 10 is I F F T (Invers
eFast Fourier Transformer
- inverse fast Fourier transformer), 11 is a reference signal generator,
12 is a multiplier, and 13 is a transmission/reception switch.

Figures 8 and 9 are similar to Figure 7 (al and fbl), respectively.
FIG. 2 is a diagram for explaining the operation of the synthetic aperture radar. In each figure, A is the transmitted signal, B is the received signal, C is the observation target, D is a certain point in the observation target C, E is the antenna beam,
F is a flying object equipped with a synthetic aperture radar.

Next, the operation of the conventional synthetic aperture radar shown in FIGS. 7(a) and 7(b) will be described. The antenna 1 is directed toward the observation target C by the antenna driving device 9 in accordance with the velocity f2 of the flying object F measured by the inertial navigation device 8. Thereafter, the transmission pulse signal generated by the transmitter 2 is radiated as a transmission signal A through the transmission/reception switch 13 and the antenna 1 toward an observation target C such as the ground surface or the sea surface. The emitted transmission signal A is reflected by the observation target C, and the received signal B
is received by antenna 1 as . Thereafter, the received signal B is input to the receiver 3 via the transmitter/receiver switch 13.

The receiver 3 amplifies and detects the high frequency received signal B, and converts it into a baseband video signal. This video signal is input to a pulse compression device 4 and subjected to pulse compression in order to improve distance resolution. This pulse compression allows the
- improve the resolution in the radial direction of the beam, that is, in the terminology associated with radar, in the range direction; R to range resolution 7 is (however, C: speed of light, τP: pulse width after pulse compression)
It is indicated by.

Now, in FIG. 7(a), the output signal of the pulse compression device 4 is input to the compensation device 5 at 411. By the way, the distance R between a point in the observation target C and the flying object F is
As is clear from FIGS. 8 and 9, it changes from moment to moment within the synthetic aperture period T. Therefore, the phase of the received signal B, in other words, the Doppler frequency at that moment also changes accordingly. By compensating for this phase fluctuation and aligning the frequency f1 based on the coordinates determined by the inertial navigation device 8, the received signal B from the observation target C can be expressed at the frequency f1 within the synthetic aperture period T. When the synthetic aperture period T8 is made large, the number of samples of the received signal B from the observation target C can be increased to 0, and the observation accuracy of the frequency f is improved, which in turn improves the angular resolution. In this way, if we let the frequency of the adjacent point of the observation target C be f, and each point in the field of view is sequentially expressed by the frequency fn, each point in the field of view can be expressed with an accuracy corresponding to the synthetic aperture period T. Points can be imaged in correspondence with their coordinates. In accordance with the instructions from the inertial navigation device 8, the phase compensation generator 5 calculates a certain distance signal separated by the pulse compression device 4 in each observation target C at an equal distance in the azimuth direction according to the operating principle of the conventional synthetic aperture radar described above. Compensate the phase of the signal from the point and change each point in the field of view to each frequency f
It outputs signals represented by 1 to fn. 0 output signal is FF
The signal is separated into frequencies f1 to fn by T6. The S width value of the signal of each separated frequency f1 to fn is calculated for each observation pair)
It corresponds to the scattering coefficient of a certain point in C. If the output signal of each channel of the FFT 6 is displayed in correspondence with the coordinates of the display surface of the display 7, the pulse compression ratio of the ZOLS compression device 4,
And a high-resolution image corresponding to the synthetic aperture period T is displayed. The synthetic aperture period T can theoretically be made infinite if the antenna drive device 9 is controlled to continue emitting radio waves in the direction of the observation target C according to the instructions of the inertial navigation device 8, but in reality ,' is limited by the range of radio waves, the time allowed for two-image reproduction, etc.

Further, in FIG. 7 tbl, the output No. 13 of the pulse compression device 4 is first inputted to the FFT 6 and frequency-separated. At this time, as described above, the received signal B from a certain point in the observation target C is output to all channels of the FFT 6 in response to the change in the Doppler frequency instantaneously within the synthetic aperture period T. However, in this case, unlike in Fig. 7 fa), each channel also includes signals 1j received from other points, but signals received from each point (signal g is stored as phase information). .

Here, based on the coordinate information of the inertial navigation controller 48, the output signal of the PFT 6 is multiplied by the reference number 1 related to the phase generated by the reference signal generator 11 by the multiplier 12. Since the phase information from each point changes from the first channel to the nth channel of the PFT 6 in accordance with the sample delay within the synthetic aperture period T, the phase information is corrected to a constant phase using the reference signal. Thereafter, when the signal is converted into a time signal by the IFFT 10, a signal at a certain time τ is separated as being from a certain point in the sharp measurement object C. The signals from each time τ to τ corresponding to each phase correspond to the signals at each azimuth point, and if these are displayed on the display 7, a high-resolution image can be obtained. The angular resolution of the displayed image is
Pulse compression ratio of pulse compression device 4 and synthetic aperture period T
Responding to ta+ is the same as in the case of ta+ in FIG. 7 above. In addition, in FIG. 7(b), there is also a method of directly processing the portion from PFT 6 to IPFT 10 in the time domain without changing the essential principle. An example of operation of these conventional synthetic aperture radars is as shown in FIG.

[Problem that the invention seeks to solve]

The conventional synthetic aperture radar described above is configured as described above, so it can obtain images with extremely high resolution, and can be used for resource exploration,
It has been proven that this type of radar can be effectively applied to creating topographic maps, etc., for example, by this type of radar installed on the American satellite SeaSat.

However, as an example of a more flexible operation, it is fine if it takes 0 hours, but you want the highest possible resolution of the image. ■ You want to monitor the ground surface in a scanning manner. ■ You want to enlarge a part of the ground surface by zooming. It is not possible to respond to requests such as: ■ Want to play back images as quickly as possible, even if the resolution is low; ■ Want to organically combine the above functions and select them according to the situation. There were problems such as: In other words, a synthetic aperture radar set to a certain mode was almost always operated in that mode alone.

The present invention was made to solve these problems, and aims to provide a synthetic aperture radar that can flexibly handle various modes according to operational requirements.

[Means for solving problems]

The synthetic aperture radar according to the present invention includes a spectrum analyzer that improves the accuracy of spectrum analysis step by step as the synthetic aperture length increases, a mode controller that operates the system in various modes according to operational requirements, and an antenna. By adding a beam controller etc. to control the direction of the beam emitted from the
This is designed to diversify the operation of the system.

[Effect]

In the synthetic aperture radar of the present invention, the mode controller is prepared with a control signal for operating the system in a mode that corresponds to anticipated operational requirements,
Quick look, scanning imaging.

The system is controlled so that modes for each operation such as zooming and high-resolution imaging can be freely switched and imaged. In addition, the control signal of the mode controller is supplied to the beam controller, pulse compression device, step conversion FFT, etc. in order to control each of the above modes, and is radiated from the antenna during the synthetic aperture period required for each mode. The beam direction is controlled and the range and azimuth resolutions are controlled to desired values, thereby increasing system flexibility and enabling imaging to meet advanced operational requirements.

〔Example〕

FIG. 1 is a block diagram showing the configuration of a synthetic aperture radar which is an embodiment of the present invention. The synthetic aperture radar shown in FIG. 1 is of a type that forms azimuth pixels in the frequency domain, and the same or equivalent parts as those of the conventional example shown in FIG. 7 are indicated using the same symbols. A detailed explanation will be omitted. In the figure, 14 is a beam controller that controls the direction of the beam emitted from the antenna 1, and 15 is a step conversion device that improves the accuracy of spectrum analysis step by step as the synthetic aperture length increases. FFT,
16 is a mode controller that operates the system in various modes according to operational requirements; 18 is /-? This is a pulse repetition controller.

Next, the operation of the synthetic aperture radar, which is an embodiment of the present invention shown in FIG. 1, will be described. Beam controller 14
controls the antenna drive device 9 using signals from the inertial navigation device 8 and the mode controller 16. The signals from the inertial navigation device 8 are signals of the position, velocity, oscillation, etc. of the flying object F, and the signals from the mode controller 16 are angle signals that change with time corresponding to a desired mode. In response to these signals, the beam controller 14 outputs a control Oi1 signal for setting the beam radiated from the antenna 1 in a desired direction via the antenna driving device 9. The course of the step-transform FFT 15 is shown in FIG. 3(a), and the basic principle of its operation is shown in FIG.
), part of the purchase includes switches 81 to SIJ.
By adding , it can be used for zooming. An example of operation of the synthetic aperture radar using the step conversion FFT 15 is shown in FIG. As shown in FIG. 4, the synthetic aperture period T is divided into several unit synthetic aperture periods τ. For each τ, the first step FF has a number of points equal to - of the final planned number of azimuth pixels NM.
T (im3 In figure (a) F F T1 , 1 ~ F F T
＋.

(denoted by M+1)) is prepared. These F'F
Signals of the same channel from T1,1 to FFTl, (M+1) are combined to create a time-series signal with a time delay from 0 to Mτ, and input to the second step FFT. The second step FFT has a number of points M corresponding to the number of the first step FFT. In the second step FFT,
The accuracy of analysis is improved by subdividing the channel interval analyzed in the first step FFT into M points. In this way, 8M spectral analysis results are obtained by combining the first step FFT and the second step FFT. Dividing the step conversion FFT 15 into a plurality of steps in this way is convenient for zooming. As shown in Fig. 4, after performing a quick look with the minimum unit synthetic aperture period τ, as the flying object F moves, the zoom is 1 with 2τ, the zoom is 2° with 3τ, etc. By proceeding with zooming step by step, it is possible to obtain an image with the highest resolution using the final maximum synthetic aperture period T. During this time, each 1st. The data to the second step FFT are τ, 2τ, 3
It can be gradually accumulated as τ,... If one N MX Indian step conversion FFT 15 is used, it is necessary to resampling the data from the beginning for each unit synthetic aperture period τ, and practical zooming is impossible. Each switch S, -SL as shown in FIG. 3 la is provided for switching the zooming step. The mode controller 16 is for switching modes according to operational requirements, and an example of its control sequence is shown in FIG. When the mode is set according to the operational requirements, the direction of the antenna 1, the pulse repetition period, the pulse compression ratio, the number of steps of the step conversion FFT 15, etc. corresponding to the mode are calculated, and the timing l11 and the bits that are each controller are calculated.・-mu controller 14
．． Output to the pulse repetition 1 controller 18, etc.

Now, each part that performs the individual operations as explained above is explained in the first section.
When combined as shown in the figure, it is possible to realize a system that flexibly combines various modes according to operational requirements. Typical operational requirements are: (1) Quick look, which allows near real-time image playback even though the angular resolution may be low; (2) Normal mode, which scans the ground surface; (3) Precision mode, where you want to take a particularly long time to obtain a high-resolution image, and (4) Zooming mode, where you can see the progress of the above. As is clear from FIG. 4, the system shown in FIG. 1 can be realized by making these values continuously variable.

In theory, even when each mode is independent, it can be easily realized only by operating the mode controller 16. FIG. 6 shows the observation status of each mode, and FIG. 6 (al indicates quick look mode, fb in the same figure) normal mode, and tc) in the same figure shows precision mode. As is clear from Fig. 6 (al), it is possible to overlap adjacent fields of view in the quick look mode, but it is possible to zoom in by setting part of the normal mode shown in Fig. 6 (bl) to the quick look mode. It is also possible to shift to normal mode while changing the setting angle of antenna 1 in the synthetic aperture radar shown in FIG.

Pulse compression ratio of pulse compression device 4, step conversion FFT
This can be realized by switching the number of steps of 15.

Also, when changing the observation distance, change the pulse repetition. All of these can be realized by using the mode controller 16 and controllers for each parameter.

FIG. 2 is a block diagram showing the configuration of a synthetic aperture radar according to another embodiment of the present invention. The synthetic aperture radar shown in Fig. 2 uses a method that processes only the normal mode in the time domain, and uses a method that forms the azimuth pixels shown in Fig. 1 above for other modes. There are 17. Here, only the differences from what is shown in FIG. 1 will be explained.
A signal is added to control the changeover switch 17, and the system is switched between the above system and the system shown in FIG. 1 according to operational requirements. Most of the conventional synthetic aperture radars are time-domain processing methods, so if a mode is to be added to a conventional product, the one shown in FIG. 2 can be realized at a lower cost.

〔Effect of the invention〕

As explained above, the present invention provides a spectrum analysis device that gradually improves the accuracy of filter analysis in synthetic aperture radar due to an increase in synthetic aperture length, and a system that operates in various modes according to operational requirements. By adding a mode controller for operation and a beam controller 4 for controlling the direction of the beam radiated from the antenna, the system operation can be diversified, making it possible to flexibly deal with various modes according to operational requirements. This has excellent effects, such as enabling imaging for high-altitude operations.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a synthetic aperture radar that is an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of a synthetic aperture radar that is another embodiment of the invention, and FIG. Step transform FFT in synthetic aperture radar in Figure 1
Figures 4 to 6 are diagrams for explaining the configuration of the synthetic aperture radar in Figure 1 and the basic principle of its operation, and Figures 7 (a) and (bl are block diagrams showing the configuration of a conventional synthetic aperture radar, and FIGS. 8 and 9 are block diagrams showing the configuration of a conventional synthetic aperture radar, respectively, and FIGS.
FIG. 2 is a diagram for explaining the operation of the bl synthetic aperture radar. Look at the diagram: 1. Antenna, 2. Transmitter, 3.
...Receiver, 4...Pulse compression device, 5...Phase compensation device, 6...FFT, 7...Display device, 8...Inertial navigation device, 9...Antenna drive device , 10...I
FFT, 11-0. Reference signal generator, 12... Multiplier, 13... Transmission/reception switch, 14... Beam controller, 15... Step conversion FFT, 16... Mode controller, 17... Changeover switch , 18... is a pulse repetition controller. In each figure, the same reference numerals indicate the same or similar parts.

Claims (3)

[Claims] (1) In a synthetic aperture radar that is mounted on a flying object such as an artificial satellite or an aircraft and obtains high-resolution images, a spectrum analysis device that gradually improves the accuracy of spectrum analysis as the synthetic aperture length increases; The antenna driving device includes an antenna driving device that can arbitrarily set the synthetic aperture length, a controller for the antenna driving device, and a mode control device that switches to real-time mode, scanning mode, high resolution mode, etc. according to operational requirements. A synthetic aperture radar characterized by: (2) In addition to the spectrum analysis device, a matched filter is provided as another channel, and the output signal of this channel can be used for mode selection of the mode control device. Synthetic aperture radar according to item 1. (3) Step conversion F in the spectrum analysis device
2. The synthetic aperture radar according to claim 1, wherein the first step FFT is connected via a switch.